Abstract: LiFePO₄ is considered as one of the most important cathod materials for lithium ion batteries, since its good thermal stability, low material cost and better enviromental compatibility. In this paper, LiFePO₄ was synthesized by hydrothermal method, with about 5% Fe atom at lithium site as determined by neutron and X-ray diffraction. In order to attain the capacity approaching the theoretical value, the high temperature annealing is often required. The samples were annealed at 450 ℃ and 700 ℃ respectively, but only little changes took place in the crystallographic structure from Rietveld refinement. This shows that iron disorder is just one of the reasons to lead low capacity for LiFePO₄ synthesized by hydrothermal method.